The invention relates to an extruder, comprising a housing with an inlet and at least two worm conveyors, consisting of a worm conveyor shaft and one or more helices provided thereon, an exhaust for the gases in the extruder housing, which as seen in the direction of transportation of the mixing worm conveyors is arranged beyond the inlet of the extruder, and a member for propelling and distributing the synthetic material, which member is located before the exhaust and on a part of the conveyor worm shaft that has no helices and which permits passage of the synthetic material in flow portions and subdivides the flow portions into smaller portions.
Such extruders in which a worm conveyor is provided with one or more helices are known per se. Within these known devices there is arranged a plate with apertures through which the mass plasticized by the conveyor mixing worms is pressed in flows which are cut into pieces by means of cutting members arranged on the mixing worms beyond the plate, while an exhaust leading to the outside is arranged for the discharge of the gases. Due to the connection of this exhaust to a vacuum pump a fast and proper de-aeration of the synthetic material can be obtained and as a consequence the processing capacity of an extruder can be considerably stepped up. This type of known device is typified by the screw-type plasticizer described in U.S. Pat. No. 3,407,438.
Such a device has the drawback that with such apertured plates or disks the jellifying effect in some synthetic materials is too great which impairs the processing of the materials. Especially in case of particular recipes it has been found that the jellification with the aforementioned plates is so great that good results cannot be obtained. Apart therefrom the maintenance of such an extruder is not easy, since it should be dismounted before the worms and plate with apertures can be removed from the extruding housing.
Another considerable drawback is that synthetic material can amass before the apertured plate, which causes the material to burn at that location and gives rise to a decrease in quality of the final product. Moreover, such a burning or combustion can make the dismounting of the extruder a matter of necessity, whereby in order to remove the apertured plate, as has been mentioned already, it is necessary to dismount the entire extruder housing which operation requires much labour.